Vegetative Compatibility Groupings of Verticillium dahliae from Cotton in Mainland China

One hundred and fourteen isolates of Verticillium dahliae obtained from cotton and eggplant in mainland China were successfully assigned to two vegetative compatibility groups (VCGs) except for one self-incompatible isolate. Eleven isolates were strongly compatible with T9, the tester strain of the cotton defoliating pathotype, forming a linear growth of wild type with abundant microsclerotia and dense mycelia between compatible nitrate-nonutilizing mutants. The remaining 102 isolates were grouped into the non-defoliating VCG2, although the strength of the reaction varied; some isolates were strongly compatible with the tester strain while others were only slightly compatible. All VCG1 isolates including T9 showed the same defoliating symptom in greenhouse inoculation tests. This study confirmed the presence of the defoliating pathotype (VCG1) of V. dahliae in mainland China.     

Vegetative Compatibility Groups in Verticillium dahliae Isolates from the Netherlands as Compared to VCG Diversity in Europe and in the USA

In a study of vegetative compatibility in Verticillium dahliae in the Netherlands, a collection of 45 isolates including representatives from woody hosts, several horticultural crops and from the soil of potato fields was examined. In addition an effort was made to compare vegetative compatibility groups (VCGs) from different countries. The results of this study indicate that VCG diversity in V. dahliae in the Netherlands is limited. Only two VCGs were detected: VCG NL-I and VCG NL-II. The former is the predominant VCG for isolates from tree hosts. However, Verticillium wilt in trees can be caused by isolates from both VCGs. It is suggested that the predominance of VCG NL-I in tree hosts is the result of the origin of the tree and the cropping history of its growing site, rather than trees being preferential hosts for isolates from this VCG. Comparison of VCG testers from the Netherlands, from several other European countries and from the USA show that in Europe two major VCGs are present. The first one, including NL-I, is compatible with USA VCG 3 and VCG 4, whereas the second one, including NL-II, is compatible with USA VCG 1 and VCG 2. These groups are not completely separated; in some cases, testers formed heterokaryons with VCG testers from both main groups. Because of the presence of these bridge isolates and because mutants from the same isolate differ in ability to form heterokaryons, it is emphasised that careful selection of isolate testers is an essential step to get a clear picture of VCG diversity.     

Genetic Relationships Among Verticillium dahliae Isolates from Cotton in Greece Based on Vegetative Compatibility

Vegetative compatibility groups of a collection of 71 Greek Verticillium dahliae isolates obtained from cotton plants were tested. Nit mutants were generated from single spore wild strains by selecting chlorate-resistant sectors on minimal medium amended with potassium chlorate, 25g/l. These mutants were tested against tester strains from the USA and Greece of the previously described VCGs 1, 2, 3 and 4. Forty-six of 71 isolates belonged to VCG2, because they were able to anastomose with the testers of this group, two isolates belonged to VCG4 and one to VCG1, while the 22 remaining strains could not be assigned to any of the identified VCGs. Our data demonstrated that wilt of cotton is caused only by V. dahliae in Greece, and VCG2 is the most commonly detected VCG. Some strains were found to be more virulent to cotton than other strains from the same VCG. This is the first report of VCG1 of Verticillium in Greece.     

Vegetative-compatibility groups in Verticillium dahliae from Israel

Nitrate-nonutilizing (nit) mutants were used to determine vegetative compatibility among 34 isolates of Verticillium dahliae from cotton, potato, olive, eggplant, chrysanthemum and tomato from 12 sites in Israel. Based on the formation of complementary heterokaryons, 33 isolates were assigned to two vegetative- compatibility groups (VCGs): one VCG contained 15 isolates from cotton, eggplant, chrysanthemum and olive; and the other VCG contained 18 isolates from potato, olive and cotton. The status of an additional isolate from tomato, which was compatible with both VCGs, remained unclear. In a limited pathogenicity test with 10 isolates, two (from tomato and eggplant) were pathogenic on tomato, eggplant and cotton; most isolates from cotton were pathogenic on cotton and eggplant only; and one from cotton was non-pathogenic. Fewer isolates were pathogenic on tomato than on cotton or eggplant. The diversity of vegetative compatibility found in our V. dahliae collection is comparable to that found in studies of American populations.     

Molecular Variability Within and Among Verticillium dahliae Vegetative Compatibility Groups Determined by Fluorescent Amplified Fragment Length Polymorphism and Polymerase Chain Reaction Markers

ABSTRACT A degree of genetic diversity may exist among Verticillium dahliae isolates within vegetative compatibility groups (VCGs) that bears phytopathological significance and is worth investigating using molecular tools of a higher resolution than VCG characterization. The molecular variability within and among V. dahliae VCGs was studied using 53 artichoke isolates from eastern-central Spain, 96 isolates from cotton, 7 from cotton soil, and 45 from olive trees in countries of the Mediterranean Basin. Isolates were selected to represent the widest available diversity in cotton- and olive-defoliating (D) and -nondefoliating (ND) pathotypes, as well as for VCG. The VCG of 96 cotton and olive isolates was determined in this present study. Molecular variability among V. dahliae isolates was assessed by fluorescent amplified fragment length polymorphism (AFLP) analysis and by polymerase chain reaction (PCR) assays for DNA fragments associated with the D (462 bp) and ND (824 bp) pathotypes, as well as a 334-bp amplicon associated with D pathotype isolates but also present in some VCG2B isolates. Isolates from cotton were in VCG1A, VCG1B, VCG2A, VCG2B, and VCG4B and those from olive trees were in VCG1A, VCG2A, and VCG4B. Artichoke isolates included representatives of VCG1A, VCG2A, VCG2B (including a newly identified VCG2Ba), and VCG4B. AFLP data were used to generate matrixes of genetic distance among isolates for cluster analysis using the neighbor-joining method and for analysis of molecular variance. Results demonstrated that V. dahliae isolates within a VCG subgroup are molecularly similar, to the extent that clustering of isolates correlated with VCG subgroups regardless of the host source and geographic origin. VCGs differed in molecular variability, with the variability being highest in VCG2B and VCG2A. For some AFLP/VCG subgroup clusterings, V. dahliae isolates from artichoke grouped in subclusters clearly distinct from those comprising isolates from cotton and olive trees. In addition, VCG2B isolates from artichoke formed two distinct clusters that correlated with PCR markers of 334 bp (VCG2B(334)) or 824 bp (VCG2B(824)). Artichoke isolates in the VCG2B(334)/2beta(334) cluster were molecularly similar to isolates of VCG1A. The molecular difference found among artichoke isolates in VCG2B correlates with virulence of isolates to artichoke and cotton cultivars demonstrated in a previous study.     

棉花黄萎病菌致病力测定及评价方法研究

 棉花黄萎病菌致病力测定及评价是抗病育种及病害综合防治的基础。本文以我国三大棉区的167个黄萎菌菌株为对象,研究致病力测定及评价中不同批次之间病情指数的校准及致病力类型划分标准等关键技术环节。结果表明,以中等致病力类型菌株Vd076为校正菌株,以感病性稳定的冀棉11为校正鉴别寄主,以校正菌株在校正鉴别寄主上病情指数达到50.0±5.0时的调查结果进行各菌株的致病力评价,可获得较好的校正效果,使不同批次试验数据具有可比性;依据聚类分析结果,制定了致病力类型划分标准,强、中、弱3种致病力类型的平均校正病指分别为﹥40.0、20.1~40.0和20.0;通过对不同鉴别寄主组合的分析,推荐陆地棉中棉所41号、豫棉21、鲁棉研28、中棉所35号、中棉所8号、冀棉11作为鉴别寄主。该研究为棉花黄萎病菌致病力变异等相关研究工作提供了技术支撑。     

Vegetative Compatibility amongVerticillium dahliae Isolates from Watermelon in Greece

Vegetative compatibility among 17 isolates ofVerticillium dahliae obtained from watermelon, originating from eight regions of Greece, was investigated using complementation tests between nitrate-nonutilizing(nit) mutants. Among 529 chlorate-resistant sectors obtained, only 107 werenit mutants. These mutants were paired with tester strains (from Greece and other countries) of previously described vegetative compatibility groups (VCGs), and also were paired in many combinations among themselves. All isolates were self-compatible. Sixteen isolates were found to belong to VCG2. Only isolate V75 could not be assigned to a VCG, because the threenit mutants obtained from it showed negative reactions with the tester strains of four VCGs and with complementary mutants from other isolates. Based on this sample, we conclude that the population ofV. dahliae from watermelon in Greece is homogeneous in respect to VCG.     

我国棉花黄萎病菌致病力分化及ISSR指纹分析

 来自我国12个省84个县（市）的棉花黄萎病菌,在PDA培养基上存在5种不同的培养类型,其中,产生微菌核较多的B型菌株为优势类群,占72.9%。长江流域的菌株培养性状变异最大,新疆棉区的变异最小。致病力测定结果和ISSR指纹图谱均将167个单孢菌株划分为强、弱、中3个致病力类型,供试菌株的ISSR指纹图谱与菌株的致病力存在明显的相关性。中等致病力类型菌株在我国占主导地位;强致病力类型的菌株主要分布在河北、河南、湖北等省;弱致病力类型菌株主要分布在新疆和江苏。     

Vegetative compatibility groups within Verticillium dahliae isolates from different hosts in Greece

Forty-four isolates of Verticillium dahliae obtained from different diseased hosts were tested by vegetative compatibility group (VCG) analysis to investigate their genetic relatedness and correlate the results with four VCGs (1, 2, 3, 4) previously described. Based on complementarity of nit mutants, only three VCGs were identified from the Greek isolates. Seventeen isolates were assigned to VCG 2 (A or B), two to VCG 3 and eight to VCG 4 (A or B). The 17 remaining isolates could not be grouped to any of the three VCGs. All isolates belonging to a distinct VCG complemented strongly with at least one of the two tester strains of that group, or with several strains of the Greek collection belonging to that VCG.     

Pathogenicity and Virulence of the Two Dutch VCGs of Verticillium dahliae to Woody Ornamentals

Two experiments were performed in two consecutive years to test whether isolates of different vegetative compatibility groups (VCGs) differ in their ability to cause disease in woody ornamentals, to study the host specificity of the isolates and to get an insight into disease development in woody hosts. A range of woody ornamental plant species, including Acer campestre, Acer platanoides, Acer pseudoplatanus, Catalpa bignonioides, Cotinus coggygria, Robinia pseudoacacia, Rosa canina, Syringa vulgaris and Tilia cordata, were root-dip inoculated with six isolates of Verticillium dahliae, belonging to the two VCGs that occur in the Netherlands (VCG NL-1 and VCG NL-2). Isolates belonging to each VCG caused severe symptoms of verticillium wilt in most plant species tested. Disease progress differed between plant species, but was generally the same for the two VCGs. No overall differences in virulence were observed between the two VCGs for external wilt symptoms, number of dead plants, or shoot length. No significant VCG × plant species interactions were present for these characteristics. However, isolates of VCG NL-1 caused more vascular discolouration than did isolates of VCG NL-2. Isolates within VCGs often differed considerably in their virulence to certain hosts, as shown by highly significant isolate × plant species interactions. Isolates were more virulent on their original host. These findings imply that VCG identification does not contribute to disease prediction for a range of woody hosts.     

Association of Verticillium dahliae and Verticillium longisporum with Chinese cabbage yellows and their distribution in the main production areas of Japan

Chinese cabbage yellows caused by Verticillium dahliae and V. longisporum is one of the most economically important diseases in Japan. Verticillium isolates from infected Chinese cabbage in Japan were identified as V. dahliae and V. longisporum based on morphological characteristics and newly developed molecular genotyping methods using group I intron of 18S rDNA, mitochondrial-SSU rDNA and cob gene. Although the two species were equally virulent to Chinese cabbage in the greenhouse, V. longisporum was more virulent in the field compared with V. dahliae. Among the 67 Verticillium isolates from Chinese cabbage, 53 were V. longisporum and considered to be the major pathogen. The isolation frequency of V. longisporum was 98?% in Ibaraki and eastern Gunma where Chinese cabbage was cropped from autumn to winter. In contrast, the frequency was 48?% in Nagano and north to west Gunma where the plant was cropped in cool summer and highland conditions and the rests were V. dahliae. This is the first report to show the different geographical distribution of V. longisporum and V. dahliae in Chinese cabbage production area of Japan.     

棉花黄萎病防治策略

黄萎病是棉花生产中的最主要病害之一,广泛分布于世界各产棉国.由于该病是土壤传播的维管束病害,防治难度较大,至今尚无特效的防治药剂,只能依靠种植抗病品种为主的综合防治措施.但是,我国目前棉花品种的抗病性只能达到抗至耐病水平,致使该病在环境条件适宜时连续流行为害.控制该病的猖獗为害,已成为棉花生产可持续发展的主要问题之一.     

Comparative Study of Genetic Diversity and Pathogenicity Among Populations of Verticillium Dahliae from Cotton in Spain and Israel

Genetic diversity and phenotypic diversity in Verticillium dahliae populations on cotton were studied among 62 isolates from Spain and 49 isolates from Israel, using vegetative compatibility grouping (VCG), virulence and molecular assays. In Spain, defoliating V. dahliae isolates (D pathotype) belong to VCG1, and non-defoliating isolates (ND) belong to VCG2A (often associated with tomato) and VCG4B (often associated with potato). The D pathotype was not identified in Israel. The ND pathotype in Israel is comprised of VCG2B and VCG4B. Isolates in VCG2B and VCG4B ranged in virulence from weakly virulent to highly virulent. The highly virulent isolates induced either partial defoliation or no defoliation. Virulence characteristics varied with inoculation method and cotton cultivar. Highly virulent isolates from Israel were as virulent as D isolates from Spain under conditions conducive to severe disease. The D pathotype is pathologically and genetically homogeneous, whereas the ND pathotype is heterogeneous with respect to virulence, VCG, and molecular markers based on single-primer RAPD and on PCR primer pairs.     

Genetic variability of tolerance to Verticillium albo-atrum and Verticillium dahliae in Medicago truncatula

Verticillium wilt caused by Verticillium albo-atrum and Verticillium dahliae is responsible for yield losses in many economically important crops. The capacity of pathogenic fungi to adapt to new hosts is a well-known threat to the durability of resistant crop varieties. In the present work, 25 Medicago truncatula genotypes from a core collection and six V. albo-atrum and V. dahliae strains were used to study the potential of non-host Verticillium strains isolated from different plant species to infect this legume plant and the plant’s susceptibility to the pathogens. The experiment was designed as factorial with randomised complete blocks and with three repetitions. The wilt symptoms caused by V. albo-atrum and V. dahliae were scored on a disease index scale from 0 to 4, during 30 days after inoculation of 10-day-old plantlets. Disease severity was quantified by maximum symptom scores (MSS) and areas under the disease progress curves (AUDPC), which integrate the time course of symptom development. Highly significant differences were observed among plant genotypes and fungal strains, and their interaction was also significant. The correlation between MSS and AUDPC was 0.86. The most severe symptoms were caused by the alfalfa strain V. albo-atrum V31-2 and the least severe by V. dahliae JR2, as shown by mean values obtained on the 25 genotypes. M. truncatula genotype TN8.3 was the most susceptible genotype by mean values obtained with the six fungal strains, whereas F11013-3, F83005.9 and DZA45.6 were highly resistant to all strains studied. The results can be used to choose parents for studying the genetics of resistance in Medicago truncatula to Verticillium strains with different levels of aggressiveness.     

Genetic Diversity of Fusarium oxysporum Isolates from Cucumber: Differentiation by Pathogenicity, Vegetative Compatibility, and RAPD Fingerprinting

ABSTRACT A total of 106 isolates of Fusarium oxysporum obtained from diseased cucumber plants showing typical root and stem rot or Fusarium wilt symptoms were characterized by pathogenicity, vegetative compatibility, and random amplified polymorphic DNA (RAPD). Twelve isolates of other formae speciales and races of F. oxysporum from cucurbit hosts, three avirulent isolates of F. oxysporum, and four isolates of Fusarium spp. obtained from cucumber were included for comparison. Of the 106 isolates of F. oxysporum from cucumber, 68 were identified by pathogenicity as F. oxysporum f. sp. radicis-cucumerinum, 32 as F. oxysporum f. sp. cucumerinum, and 6 were avirulent on cucumber. Isolates of F. oxysporum f. sp. radicis-cucumerinum were vegetatively incompatible with F. oxysporum f. sp. cucumerinum and the other Fusarium isolates tested. A total of 60 isolates of F. oxysporum f. sp. radicis-cucumerinum was assigned to vegetative compatibility group (VCG) 0260 and 5 to VCG 0261, while 3 were vegetatively compatible with isolates in both VCGs 0260 and 0261 (bridging isolates). All 68 isolates of F. oxysporum f. sp. radicis-cucumerinum belonged to a single RAPD group. A total of 32 isolates of F. oxysporum f. sp. cucumerinum was assigned to eight different VCGs and two different RAPD groups, while 2 isolates were vegetatively self-incompatible. Pathogenicity, vegetative compatibility, and RAPD were effective in distinguishing isolates of F. oxysporum f. sp. radicis-cucumerinum from those of F. oxysporum f. sp. cucumerinum. Parsimony and bootstrap analysis of the RAPD data placed each of the two formae speciales into a different phylogenetic branch.     

Spatial Patterns of Microsclerotia of Verticillium dahliae in Soil and Verticillium Wilt of Cauliflower

ABSTRACT The spatial patterns of microsclerotia of Verticillium dahliae in soil and wilt symptoms on cauliflower were determined at three sites in each of two fields in 1994 and 1995. Each site was an 8 x 8 grid divided into 64 contiguous quadrats (2 by 2 m each). Soil samples were collected to a depth of 15 cm with a probe (2.5 cm in diameter), and samples from four sites in each quadrat were bulked. Plants in each quadrat were cut transversely, and the number of plants with vascular discoloration and the number without discoloration were recorded. The soil was assayed for microsclerotia by the modified Anderson sampler technique. Lloyd's index of patchiness (LIP) was used as an indicator to evaluate the aggregation of microsclerotia in the field. Spatial autocorrelation and geostatistical analyses were also used to assess the autocorrelation of microsclerotia among quadrats. The LIP for microsclerotia was greater than 1, indicating aggregation of propagules; however, the degree of aggregation at most sites was not high. Significant autocorrelation within or across rows was detected in some spatial autocorrelograms of propagules, and anisotropic patterns were also detected in some oriented semivariograms from geostatistical analyses for microsclerotia, indicating the influence of bed preparation in the fields on pathogen distribution. The parameter estimates p and theta in the beta-binomial distribution and the index of dispersion (D) associated with the distribution were used to assess the aggregation of diseased plants at each site. A random pattern of wilt incidence was detected at 7 of 12 sites, and an aggregated pattern was detected at 5 of 12 sites. The degree of aggregation was not high. A regular pattern of wilt severity was detected at all sites. The high disease incidence (77 to 98%) observed at 11 of the 12 sites could be explained by high inoculum density.     

Vegetative Compatibility Groups in Colletotrichum coccodes, the Causal Agent of Black Dot on Potato

ABSTRACT Black dot of potato, caused by Colletotrichum coccodes, is a disease of growing economic importance, but the degree of genetic diversity and pathogenic differentiation among isolates is unknown. Using nitrate auxotrophic (Nit) mutants, we characterized vegetative compatibility groups (VCG) diversity for C. coccodes for 110 isolates originating from Israel, The Netherlands, and France. We recovered frequencies of nit1 and NitM mutant classes at 38.5 and 7.2%, respectively, and selected 12 isolates as tester isolates. Using these testers, we defined four multimember VCGs at 7.3, 35.5, 20.0, and 10.0% frequency in this sample. Thirty isolates (27.3% of all tested isolates) could not be assigned to any of the major groups, and showed only self-compatibility. The frequency of recovery of Nit mutant sectors was highest in isolates from VCG4, with 50.9 and 13.6% recovery for nit1 and NitM, respectively. However, we did not detect differences in the frequency of mutant classes among the three countries of origin. In pathogenicity tests, isolates from VCG3 were the most aggressive to potato, as expressed by high stem colonization levels and sclerotia density on root and crown. These results suggest that there is significant VCG diversity in this species and that this VCG diversity may be correlated with pathogenic characteristics or specialization.     

Vegetative Compatibility of Fusarium graminearum Isolates and Genetic Study on Their Carbendazim-Resistance Recombination in China

ABSTRACT Monoconidial isolates of 33 carbendazim-sensitive isolates and 31 carbendazim-resistant isolates of Fusarium graminearum were selected from three regions of China for vegetative compatibility group (VCG) analysis. A total of 213 and 224 nit mutants were recovered from the 33 sensitive and the 31 resistant isolates, respectively. Of all the nit mutants, the frequency of the different phenotypes was 44.6, 46.5, 5.7, and 3.2% for nit1, nit3, nitM, and nitA, respectively. VCG analysis identified 30 different VCGs among the 33 sensitive- and the 31 carbendazim-resistant isolates, with VCG diversity 0.91 and 0.97, respectively. Both, a carbendazim-sensitive and a -resistant isolate from the same field belonged to the same VCG. In all then, a total of 59 VCGs were identified among the 64 isolates with an overall VCG diversity 0.92. Direct hyphal fusion was observed in six pairs of vegetatively compatible complements, which is evidence of heterokaryon formation. It was hypothesized that carbendazim resistance could not be transferred by hyphal fusion or there is a small chance to be transferred between two compatible isolates. Three stable sexual recombinants of F. graminearum were randomly chosen from each of the three genetic crosses to study their biological properties. There were no significant differences in mycelial linear growth and pathogenicity between recombinants and their parents, but they differ in sporulation ability and capacity to produce perithecia. We concluded that sexual recombination presumably played a role in the development of carbendazim resistance under field conditions.